This invention relates to a plasma processing system for processing the surface of a semiconductor substrate (semiconductor wafer) or the like through physical action or chemical reaction of particles activated by conversion of a starting gas into a plasma.
A parallel plate ECR (electron cyclotron resonance) plasma system using UHF (ultrahigh frequency) is described in Japanese Patent Laid-Open No. 321031/1997 (corresponding U.S. Pat. No. 5,891,252). According to the invention set out in the publication, the problems to solve are to achieve processing of a high speed, a high selection ratio and a high aspect ratio, and a stable etching characteristic over a long time. For solving the problems, an electron cyclotron resonance phenomenon with an electromagnetic wave from a UHF power supply is used to form a plasma wherein the electromagnetic wave is radiated from a circular conductor plate located at a position in face-to-face relation with a substrate to be processed.
It will be noted that an etching system using a permanent magnet is disclosed, for example, xe2x80x9c1988 Dry Process Symposiumxe2x80x9d, 1988, pp. 54-57. The etching system disclosed in this literature is called magnetron RIE system wherein a permanent magnet is located over a processing chamber so as to permit RF power (13.54 MHz) only to a wafer, thereby generating a plasma on a main surface of the wafer.
We have made studies on a plasma etching system particularly shown in FIG. 13, based on the plasma processing system disclosed in the publication.
FIG. 13 is a view showing an arrangement of a parallel plate ECR plasma processing system for etching a substrate (semiconductor wafer) to be processed. In FIG. 13, a processing chamber 1 has therein a planar plate 2 provided with a shower plate 10, a dielectric substance, and a processing mount 9. A process gas is introduced into the processing chamber 1 from a gas feed port 5 provided at the planar plate 2 via the shower plate 10. A ultra-high-frequency (UHF) electromagnetic wave of 300 MHz to 1 GHz generated in a high frequency power supply 11 is introduced into the etching chamber from the planar plate 2 through a tuner 13 wherein a gas is converted to a plasma. In order to permit the UHF electromagnetic wave to be efficiently transmitted into the processing chamber, the outer diameter of the planar plate 2 and the type of dielectric substance 3 are, respectively, determined so that the high frequency is resonated at a desired mode (TM01 mode herein) between the planar plate 2 and an earth 4.
The UHF electromagnetic wave is resonated between the planar plate 2 and the earth 4 and transmitted from the periphery of the dielectric substance 3 toward the processing chamber 1. For high efficiency discharge, a solenoid coil 17 for generating a magnetic field is disposed around the processing chamber 1, and a coil current is so controlled that a magnetic field ranging from 0 gauss to 360 gausses is generated beneath the shower plate 10. Eventually, there is generated a high density plasma having an electron density of 1011 electrons/cm3 or over by use of electron cyclotron resonance (ECR). A substrate 8 to be processed is set on the processing mount 9 and etched by means of the plasma. The etching gas is introduced into the etching chamber 1 through a gas feed port 5 and exhausted to outside of the etching chamber by means of an exhaust pump.
A high frequency bias of from 100 kHz to 15 MHz is applied from a high frequency power supply 15 via a tuner 16 to the processing mount 8 on which the substrate 8 to be processed is mounted. The distance between the substrate 8 to be processed and the shower plate 10 can be changed from 20 mm to 150 mm by use of a vertically moving mechanism for the mount 9. The processing mount 9 has such a structure that enables one to provide a focus ring 7 with a width of about 30 mm around the substrate 8 to be processed. The focus ring 7 is so arranged that a high frequency is applied thereto as branched from 10 to about 50% of the high frequency power applied from the high frequency power supply 15 to the substrate 8 to be processed. Usually, the focus ring 7 is made of aluminium (Al) at the lower portion thereof and crystalline silicon (Si) at the upper portion thereof, and may be made of impurity-doped Si, silicon carbide (SiC) or Al at the upper portion thereof.
The planar plate 2 may be applied with a frequency (ranging from 10 kHz to 27 MHz), different from that from the high frequency power supply 11, from a high frequency power supply 12 via a tuner 14. This shower plate 10 is in contact with the planar plate 2, and a coolant is introduced into the planar plate 2 from a coolant inlet 6 to control the temperature of the shower plate 10.
In the system shown in FIG. 13, uniformity is optimized by changing an electric current mainly passing through the solenoid coil 17 to control the position of magnetic field intensity serving as an ECR condition.
In this arrangement, the plasma can be generated in a high efficiency, and the thus generated plasma is transported to the surface of a substrate to be processed with the aid of a magnetic field in an efficient manner, thus enabling one to make highly efficient processing. Moreover, the arrival of the plasma at the processing container walls is suppressed by the action of the magnetic field, thus making it possible to suppress the variation in processing conditions as will be accompanied by the change in the state of the processing container walls.
Our studies revealed that further problems to solve were involved in the above-stated plasma processing system.
The plasma processing system shown in FIG. 13 has no problem on uniformity when the ion current flux ranges from low to medium levels and exhibits a linear characteristic relative to making power. However, when the making power is increased to obtain a high plasma density (of 1011/cm3 or over), the wafer uniformity of the etching rate becomes 10% or over, and thus, a further improvement has been necessary. More particularly, the distribution of the etching rate is such that, as shown in FIG. 5, the rate becomes smaller only in the vicinity of the wafer center. This is ascribed to the uniformity of the plasma density, which has been a problem to solve.
In FIG. 3, there are shown a magnetic field vector (a) and an electric field vector of an electromagnetic wave by the influence of the solenoid coil 17 beneath the planar plate in the etching system shown in FIG. 13. It has been uncovered that when using the etching system shown in FIG. 13, the angle of intersection between the direction of electric line of force (electric field vector (b)) and the magnetic line of flux (magnetic field vector (a)) is smaller at the center of the planar plate, thus the efficiency of plasma generation being low. More particularly, there is a portion, in which the magnetic field vector (a) is coincident with the electric field vector (b), at the center of the planar plate. Thus, this is considered to cause the non-uniformity under such high plasma density conditions as mentioned above.
An object of the invention is to provide a parallel plate ECR plasma processing system, which ensures uniform processing of a substrate to be processed in a low density to high density plasma condition.
Another object of the invention is to provide a method for making a semiconductor device, which includes the etching step capable of reducing an in-plane variation of a semiconductor wafer.
The parallel plane ECR plasma system of the invention includes a solenoid coil as a first magnetic-field-forming means and a second magnetic field-forming means located in the vicinity of a planar plate so as to from a local magnetic field. The magnetic field formed by the first magnetic field-forming means is influenced by the magnetic field from the second magnetic field-forming means so that an angle of intersection of an electric line of force and a magnetic line of flux caused by an electromagnetic wave is locally changed. Eventually, the interactions of the electromagnetic wave and the magnetic field become substantially equal over the entire surface beneath the planar plate, enabling one to generate a uniform plasma.
When the polarity of the magnetic field formed by the first magnetic filed-forming means and the polarity of the magnetic field formed by the second magnetic field-forming means are opposite to each other, the effect of increasing the angle increases. In this way, the degree of the interaction of the magnetic field and the electromagnetic force beneath the center of the planar plate increases, thereby ensuring a uniformity of 10% or below at a high plasma density (of 1xc3x971012/cm3 or over). In addition, when the frequency of the electromagnetic wave used for plasma generation ranges from 80 MHz to 500 MHz, the intensity distribution of an electric field vector of the electromagnetic wave can be made uniform with respect to a substrate of a large diameter (diameter: 300 mm) to be processed, thus making it possible to generate a uniform plasma with the aid of the above-mentioned magnetic field control.
The parallel plate ECR plasma system according to one embodiment of the invention is characterized by comprising a processing mount for mounting a substrate to be processed in a processing container, a planar plate capable of radiating an electromagnetic wave at a position in face-to-face relation with the substrate to be processed, a first magnetic field-forming means for forming a magnetic field, which is disposed at an outside or inside of the processing container so as to convert a given type of gas to a plasma by aid of the electromagnetic wave, and a second magnetic field-forming means located in the vicinity of the planar plate for forming a magnetic field different from the magnetic field formed by the first magnetic field-forming means, wherein a direction of a magnetic line of flux in the vicinity of the planar plate is controlled by combination of the magnetic field formed by the first magnetic field-forming means and the magnetic field formed by the second magnetic filed-forming means.
According to another embodiment of the invention, there is provided a parallel plate ECR plasma system, which is characterized by comprising a processing mount for mounting a substrate to be processed in a processing container, a planar plate capable of radiating an electromagnetic wave at a position in face-to-face relation with the substrate to be processed, a magnetic field-forming means for forming a magnetic field, which is disposed at an outside or inside of the processing container so as to convert a given type of gas to a plasma by aid of the electromagnetic wave, and means for controlling a direction, on the planar plate, of the magnetic field formed by the magnetic field-forming means, which depends on the magnitude and direction of an electric field vector of the electromagnetic wave formed on the surface of the planar plate, wherein the given type of gas is converted to a plasma for processing the substrate to be processed.
According to a further embodiment of the invention, there is provided a parallel plate ECR plasma system, which is characterized by comprising a processing mount for mounting a substrate to be processed in a processing container, a planar plate capable of radiating an electromagnetic wave at a position in face-to-face relation with the substrate to be processed, a magnetic field-forming means for forming a magnetic field, which is disposed at an outside or inside-of the processing container so as to convert a given type of gas to a plasma by aid of the electromagnetic wave, and means for controlling a distribution of a magnetic field on the surface of the planar plate, depending on a distribution of an electric field of the electromagnetic wave on the surface of the planar plate, in such a way that an efficiency of generation of the plasma formed through the interaction of the electric field of the electromagnetic wave formed on the surface of the planar plate and the magnetic field formed by the magnetic field-forming means has a difference within xc2x120% in a region of not smaller than 50% of the entire surface of the planar plate, wherein the given type of gas is converted to a plasma, with which the substrate to be processed is processed.
According to a still further embodiment of the invention, there is provided a parallel plate ECR plasma system, which is characterized by comprising a processing mount for mounting a substrate to be processed in a processing container, a planar plate capable of radiating an electromagnetic wave at a position in face-to-face relation with the substrate to be processed, a magnetic field-forming means for forming a magnetic field for generating a plasma by aid of the electromagnetic wave, and means for controlling a distribution of a magnetic field on the planar plate so that a product of a sine of the angle, on the planar plate, between the electric field vector of the electromagnetic wave and the magnitude of the electric field vector of the electromagnetic wave formed on the surface of the planar plate has a difference within xc2x120% in a region of not smaller than 50% of the entire surface of the planar plate, wherein a given type of gas is converted to a plasma, with which the substrate to be processed is processed.
According to another embodiment of the invention, there is provided a method for manufacturing a semiconductor device by use of a plasma processing system which comprises a processing mount for mounting a substrate to be processed in a processing container, a planar plate capable of radiating an electromagnetic wave at a position in face-to-face relation with the substrate to be processed, a first magnetic field-forming means for forming a magnetic field, which is disposed at an outside or inside of the processing container so as to convert a given type of gas to a plasma by aid of the electromagnetic wave, and a second magnetic field-forming means located in the vicinity of the planar plate for forming a magnetic field different from the magnetic field formed by the first magnetic field-forming means, wherein a direction of a magnetic line of flux in the vicinity of the planar plate is controlled by combination of the magnetic field formed by the first magnetic field-forming means and the magnetic field formed by the second magnetic field-forming means, the method comprising the step of etching an insulating film formed on a main surface of the semiconductor wafer.
According to still another embodiment of the invention, there is provided a method for manufacturing a semiconductor device, which comprising the steps of (a) forming an insulating film on a main surface of a semiconductor substrate, (b) forming a mask having a given pattern on the insulating film, (c) placing the semiconductor substrate, on which the mask has been formed, on a processing mount in a processing container, radiating an electromagnetic waver from a planar plate in face-to-face relation with the semiconductor substrate surface on which the mask has been formed, forming a magnetic field so that a plasma is generated between the semiconductor substrate surface and the planar plate by aid of the electromagnetic wave, controlling a direction of the magnetic field on the planar plate, etching the insulating film at portions where the mask is not formed, and forming an opening in the insulating film; and (d) burying a conductor layer in the opening.